In modern engines, the air-fuel ratio (AFR) in the cylinder may be controlled close to stoichiometry to maintain high emission conversion efficiency of the exhaust catalyst system. One of the issues that affects the accuracy of AFR regulation is that a fraction of injected fuel sticks to the port walls, in so-called “puddles.” Fuel from the puddles evaporates at a rate that depends on many factors including wall temperature, manifold pressure, and fuel volatility. Engine control strategies may include compensation for the fuel-puddling (also called wall-wetting) effect, but the complexity of the underlying physics makes the strategy complicated and the calibration process time consuming. Part of the complexity is due to the varying volatility of fuels available at the pump (e.g., depending on the season and location) and the requirement that some vehicles run on flex fuels which can be a variable mixture of gasoline and ethanol (C2H5OH), with up to 85% percent of ethanol. The blending leads to different behavior of the fuel in terms of vaporization and puddle formation.
Current approaches address the physics of fuel vaporization by modeling, for example, multiple puddles, and multiple fuel components. The fuel components might include the standard gasoline components (e.g., pentane, iso-octane, etc.) as well as ethanol for flex fuel applications. Another set of approaches are based on simpler “black box” models, for which the parameters are determined by matching the model output to the observed (e.g., measured) air-fuel ratio.
The inventors of the present application have recognized a problem in such previous solutions. The multi-component, multi-puddle models are complex and typically require a significant amount of computational resources to run in real time. They are also nonlinear, and hence, not conducive for transient fuel puddle compensation. The black box models rely on numerous calibrations to attempt to compensate for the fuel-puddling. The calibrations are typically time intensive and may not effectively compensate for the port puddling effect because the physics of the process is not captured well by the simplified model. In particular, these models are not capable of tracking the fraction of ethanol in the port puddle as opposed to the fraction of ethanol in the tank. Consequently, an effective transient fuel compensation may not be achieved, thereby degrading engine emissions.
Accordingly, in one example, some of the above issues may be addressed by a method of adjusting an amount of fuel injection to an engine based on an ethanol content of fuel in a port puddle. Further, in some embodiments, the adjustment may be further based on the percent ethanol of the injected fuel. Further, in some embodiments, such an approach may include determining the amount of fuel evaporated from the puddle based on selected components of the fuel and their respective vapor pressures via a multi-component fuel model. The vapor pressures may be identified via text-book values and, hence, may be accessed via a look-up table, for example, as opposed to via calibration. By reducing the amount of calibratable tables referenced in determining a fuel injection compensation, an amount of a fuel injection may be more efficiently and rapidly determined, as described in more detail herein.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.